1350-1400;Middle Englishcontrevailen < Anglo-Frenchcountrevail-, tonic stem (subjunctive) of countrevaloir to equal, be comparable to < Latin phrase contrā valēre to be of worth against (someone or something). See counter-, -valent

late 14c., "to be worth as much as," also "to prevail against," from Anglo-French countrevaloir, Old French contrevaloir "to be effective against, be comparable to," from Latin phrase contra valere "to be worth against" (see contra- and valiant). Related: Countervailing.